In general, the right shoulder attempts to go up and over where the left shoulder was when it was extended after the toss. What really happens is the left shoulder slides out and to the left to accommodate the right shoulder "leapfrog". I think it is really well explained in revolutionarytennis.com.

But here is a very good example of the cartwheel method. Watch Krajicek hit his flat bombs:

Thanks, I've been doing a lot of research, I wasn't pushing out my hip, not pulling my right shoulder back even more. It's working, unjust need to get muscle memory on those two things and then I'll move on to other mechanics

Everyone has their own slightly different variation on their wind up. You may want to try breaking down your motion at first and put a towel on the ground at the service line and kneel down on th right knee to serve from there with the racket already on their back. That simplifies the motion taking the legs out of the equation for the time being. Then it should be simpler to work on timing and the position of the ball toss, especially on developing a lethal second serve. I hope that helps. If your having trouble incorporating your legs into the serve watch how Rodger warms up his serve in practice an how much his body turns around his torso so that his left side is almost moving away from the ball (with an axis down his spine) as he is about to hit it. Its a balancing twisting motion and that will help avoid muscling the ball and it will give everything alot more pace if you can incorporate that body turn. That turning, torquing motion is why the racket moves faster when the elbow is bent in to start off with not so much the jumping. Before Rafa was muscling the ball over and stressing out his shoulder while not even getting much pace on the ball. Does that make sense?

Good timing will not necessarily guarantee a faster serve. It will probably lead to more consistent serve.

One simple tip for a faster serve is "start loose, finish loose". Make sure you start your serve prep motion with a loose arm, and finish the motion with loose arm. Hold your grip loosely and only tighten it on your upswing before contact with the ball. Complete the follow through motion all the way around your left hip. Many players appear to 'finish' the motion (or 'think' they 'finish' the motion), but in many cases the follow through can actually go a little more to their left hip. That extra finish gives you a bit more speed and that extra finish distance can only be achieved when you're swinging with very loose arm.

The other factor that limits speed is that some people get out of the 'trophy position' a little too fast when the ball is up on the peak of the toss. Holding that trophy position with your right hand just a tad longer allows you to get that whipping motion with your right arm where you will get your racquet to your back (nearly touching your spine) and then whipping it up hitting through the ball. The wrist pronation will also add a few mph.